1. Field of the Invention
This invention relates to editing control apparatuses, and more particularly, to an editing control method and apparatus for video tape recorders which permit accurate prerolling of the video tapes prior to editing.
2. Description of the Prior Art
In the editing of a video tape, a portion of the video tape to be edited has recorded thereon video information from another video source. The other video souce can be, for example, a video camera or a video signal recorded on another video tape. When the source of the video information is a video signal recorded on another video tape, one video tape recording and/or reproducing apparatus is required for each tape in order to produce an edited video tape.
When two video tapes are used in editing, they must be accurately positioned at respective preroll points, i.e., points on the video tapes located before the editing start points. After the video tapes are positioned at the respective preroll points, the video tapes are advanced in synchronism until the editing start points are reached and the actual editing operation begins.
In order to operate two video tape recording and/or reproducing apparatuses in synchronism, two types of signals recorded on the video tapes have been utilized. One type of signal is a time code signal such as the Society of Motion Picture and Television Engineers time code signal (SMPTE) or the like. Alternatively, control signals associated with the video tracks recorded on the video tapes have been used for synchronization.
The use of control signals to synchronize the video tapes has significant difficulties. While the tapes are moving, the synchronization of the video tapes can be detected quite accurately. However, when the direction of tape travel is changed, or pinch rollers used in driving the tape are intermittently engaged therewith so that the tape is not continuously advanced, the control signals can not be accurately detected, and, accordingly, it cannot be determined whether two tapes are operating in synchronism.
When time code signals are utilized to synchronize the editing of two video tapes, a unique address location on each tape can be detected even when the tape is at rest. However, time code signals are generally placed on the video tape during the recording process, and are consecutively numbered. If the tape is stopped, for example, during recording, the time code signals recorded on the tape are not consecutive. Thus, upon playback, precise time differences between the two tapes can not be detected accurately, making it difficult to synchronize the video tapes during editing.